The conventional electrocardiograph and the bioelectrode pad are known for example from a patent document 1 which is previously proposed by an applicant of this patent application. In the electrocardiograph mentioned above, it is possible to measure the electrocardiac signal without being disturbed by the body motion noise by: using a plurality of bioelectrode pads each having a plurality of electrodes having different areas respectively which are contacted with a skin surface of a specific portion of living body respectively; measuring an original electrocardiac signal by contacting the bioelectrode pads with the skin surface of living body and obtaining a difference between signals supplied from either one electrodes of these bioelectrode pads; measuring a signal of the body motion noise by obtaining a difference between a signal supplied from the electrode having a relatively small area and a signal supplied from the electrode having a relative large area, with respect to respective bioelectrode pads; and removing a low frequency component of the signal of the body motion noise from the original electrocardiac signal. In this case, the signal of the body motion noise is generated, since a polarization potential and impedance, which generate between the electrode and a conductive gel or between the conductive gel and the skin surface, are varied due to the body motion.